The minute it feels like you have to push the wood into the blade as opposed to it "melting" into the blade, or you start have difficulty controlling the blade, time to change. And like all things there are a lot of factors. You cannot put a time limit on it. What your are cutting, What wood you are using, what type blade you are using. I Probably, and I have never timed it, just a guess, but I would say on average I may get 20 minutes out of a blade. But again I do not set a timer, when I feel in the slightest that I am having to work to get the blade to go where I want, it is time for me to change. Right now I am cutting in 1/2" Monkey Pod, a little harder than Popular, maybe, but what I am cutting I want to be precise, I am using a #1 size blade and I have probably changed the blade every 10 minutes at the most. That is just me, your mileage may vary as they say. You may not want to go by what I say,, I have broken lots and lots of blades! But I am often trying different blades, different technics, different woods..expect to break blades.